Maybe because of Blissey holding Heavy Duty Boots?
commented 5 hours ago by PorygonZangoose
leftovers and heavy duty boots are more valuable than the defence for the majority of ladder, makes it harder to wear down which is valuable for game in game out. Chansey's better bulk used to be more important.
commented 3 hours ago by PX ™
I have no idea tbh
Probably because of heavy duty boots, like what PX and PorgonZangoose said
commented 7 minutes ago by R3BEL
Simple: Chansey has to hold Eviolite to be viable.
Blissey has more versatility in the item department. Yes, Chansey is bulkier with Eviolite, but on every switch in it takes Stealth Rock / Spikes damage, and this is quite hindering due to Natural Cure. Chansey is more scared of constant switching, allowing Pokemon to take advantage of this and status it. Plus, such easy chip damage on such a sturdy wall is really not ideal for the user of the wall.
This is why Blissey, in this metagame, is considered better. It usually runs Heavy-Duty Boots, allowing it to use Teleport and cure its status with Natural Cure without taking entry hazard damage. As PX pointed out, Leftovers are also viable, as they indirectly cancel out entry hazard damage.
So, basically, Chansey may have better bulk with Eviolite, but Blissey taking no damage or passively healing the damage from entry hazards is more valuable than sheer bulk.
Hope this helps! :)